When you say never enough. Enough of what speed or power coming out of the corner? Are you on 6" rear tires or 8".

How big are the tracks that you run on.

On mine I run a 8 on the engine 5 on the tranny for pulleys and any where from 13 to 16 on the tranny and 40 to 46 on the axle. Now that I've gone to 6" rear tires I've gone as high as 18 tooth on the tranny. This all depends on track size and what the track surface is made of. This will also influence gearing.

PJG56 is right. If you have one of the 700's that has 23/27 in "3rd", your total drive ratio is 5.179. Which is close, but an average for GP is 4.75-5.0:1 overall drive ratio. If you had 25/25 gearset, your total drive ratio would be 4.4118:1. That would mean you need to be somewhere in between those two numbers.

I am curious to know what the transmission's assembly number is? We might can help you with what gears you have. Next bet, which I would recommend anyway, is to split the case and count teeth. Some transmissions didn't have the 25/25 set at all, and some had the 25/25 gearset in 5th. There are literally hundreds of combinations.

we run a bit higher (numerically lower) ratio on our Mod-XR. We are in the 4.50 range and at our last race was at 4.22. We do however run a Kawasaki 540 and keep it governed at closer to 3560. It makes more power there than if we push it up to 3650. Plus we never need to worry about failing post race tach check.

Drop your axle sprocket to 44 and you will have a gear ratio of 4.85 Your ratio as it sits is 5.02:1 which might be a little steep. Race in 5th gear, your 25/25 gear set, top speed about 35 MPH depending on tire size (16") and RPM of engine (3650)